One conventional method of cooling the walls of combustion chambers of gas turbine engines uses cooling rings which are positioned between and secured to axially spaced wall sections. These cooling rings are provided with a plurality of relatively large apertures arranged in a row, or a number of rows of relatively small apertures. These apertures direct a flow of cooling fluid onto the inner surface of the wall to form a film of cooling fluid which protects the wall from the high temperatures produced in the combustion chamber. However, such cooling rings are relatively wasteful of cooling fluid.
A further problem with the cooling rings is that the thermal gradients produced across the cooling ring lead to cracking of the cooling ring and the large numbers of cooling apertures allows easy propagation of the crack and eventual failure of the cooling ring.
A further conventional method of cooling the wall of combustion chambers of gas turbine engines uses walls which are formed from two or more laminae which are secured together to form internal passages therethrough for transpiration cooling of the wall by a cooling fluid. The cooling fluid is then directed through apertures out of the wall to from a cooling film of fluid on the inner surface of the wall. These arrangements are more efficient than the cooling rings using approximately a third of the cooling fluid, but the inner surface of the wall tends to become relatively hot because of ineffective film cooling due to the apertures being arranged normal to the inner surface and being spaced by relatively large distances.